U.S. Pat. No. 4,432,410 and the corresponding French published patent application No. FR 2 481 791A describe a radiator of the above kind, comprising a fluid manifold having a tube branch for inlet or outlet of a cooling fluid, and a bundle of tubes the ends of which are open into the said fluid manifold, together with a bulkhead formed with an aperture and dividing the fluid manifold into a first chamber and a second chamber. The ends of a first group of the tubes, and the said inlet or outlet tube branch, are open into the first chamber, while the complementary group of tube ends is open into the second chamber. The radiator also includes a first masking or valve member for opening the aperture in the bulkhead, this masking member being movable by an actuator between an opening position and a closing position. In the opening position, the masking member enables the fluid passing into the fluid manifold through the inlet tube branch, or leaving it through the outlet tube branch, to be able to pass directly from the first chamber to the second chamber or vice versa. In the closing position, the masking member forces the fluid to pass through the tubes of the first group.
In that known radiator, the flow control device defined by the first masking member and the actuator serves the function of the traditional thermostat which is commonly placed on the outside of the radiator. Its effect is to suppress the circulation of the fluid in all or some of the tubes of the radiator when the engine is cold, and to set up normal circulation in all the tubes once the engine is sufficiently hot, i.e. after a certain running time.
In order to optimise the engine power output, it is desirable that it shall work at a constant temperature, which makes it necessary to cause the efficiency of its cooling to vary as a function of the heat energy which it emits, and therefore as a function of its loading. In order to make the cooling efficiency vary, and thus to regulate the temperature of the engine, it is possible to act on various parameters, and in particular on the flow of the fluid passing through the tubes of the radiator. To this end it is known to arrange, in series with the radiator, a flow regulating valve controlled by a cooling fluid temperature sensor placed at the fluid outlet of the engine. The use of such a regulating valve complicates the construction of the cooling circuit. In addition, rotary valves, such as are commonly used, do not have a sufficiently progressive regulating action at low rates of fluid flow.